Commit 0ae2062e authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'locking-futex-2025-03-23' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull futex update from Thomas Gleixner:
 "A single update for futexes:

  Use a precomputed mask for the hash computation instead of computing
  the mask from the size on every invocation"

* tag 'locking-futex-2025-03-23' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  futex: Use a hashmask instead of hashsize
parents 0f404646 e3924279

kernel/futex/core.c

+11 −10
Original line number Diff line number Diff line
@@ -50,10 +50,10 @@ 
 */

static struct {

	struct futex_hash_bucket *queues;

	unsigned long            hashsize;

	unsigned long            hashmask;

} __futex_data __read_mostly __aligned(2*sizeof(long));

#define futex_queues   (__futex_data.queues)

#define futex_hashsize (__futex_data.hashsize)

#define futex_hashmask (__futex_data.hashmask)





/*
@@ -119,7 +119,7 @@ struct futex_hash_bucket *futex_hash(union futex_key *key) 
	u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,

			  key->both.offset);



	return &futex_queues[hash & (futex_hashsize - 1)];

	return &futex_queues[hash & futex_hashmask];

}
@@ -1127,27 +1127,28 @@ void futex_exit_release(struct task_struct *tsk) 


static int __init futex_init(void)

{

	unsigned long hashsize, i;

	unsigned int futex_shift;

	unsigned long i;



#ifdef CONFIG_BASE_SMALL

	futex_hashsize = 16;

	hashsize = 16;

#else

	futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());

	hashsize = roundup_pow_of_two(256 * num_possible_cpus());

#endif



	futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),

					       futex_hashsize, 0, 0,

					       hashsize, 0, 0,

					       &futex_shift, NULL,

					       futex_hashsize, futex_hashsize);

	futex_hashsize = 1UL << futex_shift;

					       hashsize, hashsize);

	hashsize = 1UL << futex_shift;



	for (i = 0; i < futex_hashsize; i++) {

	for (i = 0; i < hashsize; i++) {

		atomic_set(&futex_queues[i].waiters, 0);

		plist_head_init(&futex_queues[i].chain);

		spin_lock_init(&futex_queues[i].lock);

	}



	futex_hashmask = hashsize - 1;

	return 0;

}

core_initcall(futex_init);